Primer compositions that promote the adhesion of overcoatings onto substrates are known in the art. They are particularly useful in articles requiring the bonding of organic materials to inorganic substrates. The resulting adhesion of the overcoating, however, is frequently less than is necessary for the desired use.
Silica organosols have been added to organic polymer type protective coatings to strengthen and improve the adhesion of the coating to a substrate. For this purpose, U.S. Pat. No. 2,692,867 discloses the use of silica organosols of silica particles having absorbed on their surface a long hydrocarbon chain substituted ammonium ion and U.S. Pat. No. 2,801,185 discloses the use of silica particles having a coating of any substance reactive with the silica surface, preferably an alcohol. The use of such a composition is described only as the exposed coating itself and is not disclosed as a primer.
Antireflective coatings of inorganic oxides on optical articles are described in Assignees copending patent applications U.S. Ser. No. 035,272 filed Apr. 2, 1987 and U.S. Ser. No. 910,250 filed Sept. 19, 1986. Coating compositions comprising a sol of a metal oxide and optionally a binder resin are disclosed. The use of these compositions as a primer is not disclosed.
Assignees copending application U.S. Ser. No. 40,930 filed Apr. 21, 1987 describes the use of sol coating of inorganic oxides on polymeric substrates as subbing layers (primer layers) for photographic hydrophilic colloid silver halide emulsions.
There is disclosed in Japan Kokai Tokkyo Koho JP 82 25, 371 (Chem. Abstracts 97, 74008h (1982)) the use as a primer for concrete substrates of a composition of emulsions of synthetic polymers or synthetic rubbers and colloidal silica. Such a primer composition is slow drying and not at all suitable for modern construction where speed of application and readiness for placement of a top layer is important as is the situation in much housing development and highway marking.
The prior art, thus, does not teach a composition suitable for the rapid promotion of adhesion of a polymeric coating, e.g., paints, lacquers, tapes and the like onto inorganic surfaces, e.g., concrete, ceramics, porcelain, glass, bricks, stone, metal and the like or the adhesion of one inorganic substrate to another inorganic substrate.